Narrow spectral linewidth operation in DFB, DBR-DC-PBH laser diodes
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Abstract:
Optical heterodyne communication systems1 have been proposed as a possible transmission method to obtain ultralong repeater spacings. Such systems require signal and local oscillator highly coherent light sources. A He-Ne gas laser or external cavity laser diode has been used in prototype heterodyne experiments. However, a practical system will need single-longitudinal-mode (SLM) semiconductor lasers because they have many advantages, such as the small device size, spectral stability to ambient temperature fluctuation, and high reliability.Keywords:
Laser linewidth
Heterodyne detection
Heterodyne (poetry)
Superheterodyne receiver
Heterodyne (poetry)
Heterodyne detection
Backward-wave oscillator
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A semiclassical approach is used to calculate the principle for heterodyne detection utilizing two optical detectors. These calculations show that excess-noise in the local-oscillator can be canceled and the balanced-detector optical heterodyne detection requires less local oscillator power compared with the traditional single-detector optical heterodyne detection. An experimental demonstration of excess-noise cancellation is reported.
Heterodyne detection
Heterodyne (poetry)
Semiclassical physics
Noise power
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A sensitive heterodyne receiver has "been constructed for use in the submillimeter wave region. The application of a laser as a local oscillator (LO) in the fundamental mixing mode greatly improves the sensitivity compared to systems with klystron LO's in the harmonic mixing mode, especially in the 1 THz region. The possibilities for application in submillimeter spectroscopy are demonstrated with a tunable receiver for the region around 891 GHz employing an HCN laser as a LO. The high sensitivity obtained with this system shows good prospects for spectroscopy in the 1-5 THz region.
Superheterodyne receiver
Heterodyne (poetry)
Klystron
Heterodyne detection
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Optical heterodyne detection of partially coherent cross-spectrally pure radiation is considered. A general formulation of the problem based on the photodetection statistics is presented first. Effects of temporal and spatial coherence of the signal on the heterodyne detection efficiency are then presented. Four limiting cases classified by the signal radiation coherence properties are considered in detail. The heterodyne antenna property, local oscillator (LO) laser requirement, and effects of radiation statistics on the heterodyne efficiency are also considered.
Heterodyne detection
Photodetection
Heterodyne (poetry)
Superheterodyne receiver
Coherence time
SIGNAL (programming language)
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We present the theoretical and detailed experimental characterizations of photothermal heterodyne imaging. An analytical expression of the photothermal heterodyne signal is derived using the theory of light scattering from a fluctuating medium. The amplitudes of the signals detected in the backward and forward configurations are compared and their frequency dependences are studied. The application of the photothermal heterodyne detection technique to the absorption spectroscopy of individual gold nanoparticles is discussed and the detection of small individual silver nanoparticles is demonstrated.
Heterodyne (poetry)
Heterodyne detection
Photothermal spectroscopy
Photothermal effect
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We demonstrate heterodyne detection of CARS signals using a cascaded phase-preserving chain to generate the CARS input wavelengths and a coherent local oscillator.The heterodyne amplification by the local oscillator reveals a window for shot noise limited detection before the signal-to-noise is limited by amplitude fluctuations.We demonstrate an improvement in sensitivity by more than 3 orders of magnitude for detection using a photodiode.This will enable CARS microscopy to reveal concentrations below the current mMolar range.
Heterodyne (poetry)
Heterodyne detection
Photodiode
SIGNAL (programming language)
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Superheterodyne receiver
Heterodyne (poetry)
Heterodyne detection
Noise temperature
Noise-equivalent power
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Frequency-division-multiplexed (FDM) optical networks with fast-tuning optical components allow multiple logical connections to be maintained by using a single transmitter and receiver. Heterodyne detection using a fast frequency-hopping local oscillator offers a fast-tuning receiver for such applications. A heterodyne receiver can be more selective and orders o í magnitude faster than conventional optomechanical devices such as piezo-driven Fabry-Perot filters. In this work a heterodyne receiver with a wavelength-tunable local-oscillator (LO) laser is used with a fast-tuning laser transmitter to select arid demodulate either one of two 1.244-Gbit/s signals multiplexed in both time and optical frequency. Channel switching times of <13 ns and channel dwell times of 1.953 µs are demonstrated.
Heterodyne detection
Heterodyne (poetry)
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The nonlinear four-frequency heterodyne detection has been analysed theoretically in experiment. The nonlinear four-frequency heterodyne detection was realized and the results obtained coincides with expected one in this paper, we suggest multifrequency heterodyne detection systems, which can be used for finding out objectives, imaging contours and other application, etc.
Heterodyne (poetry)
Heterodyne detection
Detection theory
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A traditional heterodyne detector, as a phase-insensitive device, suffers the well-known 3 dB noise penalty caused by image sideband vacuum. In contrast, a heterodyne detector with a bichromatic local oscillator, as a phase-sensitive device, should be exempted from the 3 dB noise penalty, in spite of the existence of the image sideband vacuum. Assuming coherent light at the input, we develop in this work a theory to describe the quantum nature of the phase-sensitive heterodyne detector, in a good agreement with experiment. The absence of the quantum noise of the image vacuum modes in the heterodyne detector may be explained by that the studied detector senses only a single field of light, i.e., the signal field, according to the theory developed.
Heterodyne (poetry)
Heterodyne detection
Quantum noise
Compatible sideband transmission
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